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Abstract:

A planetary gearbox, for an automatic transmission of a motor vehicle,
comprising two stages, each provided with a sun gear, a ring gear and
interposed planetary gears. The ring gear of the first planetary stage
also forms the sun gear of the second stage, and the planetary gears of
both stages are guided by a common planet carrier, produced from a
casting material, which accommodates the planetary gears of the first
stage at an axial offset position to the planetary gears of the second
stage. The planet carrier is designed as one-piece such that pockets are
respectively disposed in the planet carrier for receiving the planetary
gears of the first stage at an offset angle, in the circumferential
direction, to the pockets for receiving the planetary gears of the second
stage, so that it is possible to form the pockets during casting using
slides.

Claims:

1-7. (canceled)

8. A planetary gearbox for an automatic transmission of a motor vehicle,
the planetary gearbox comprising: first and second stages (1, 2), each
stage being provided with a sun gear (3), a ring gear (5, 9) and
interposed planetary gears (4A-4C, 8A-8C), the ring gear (5) of the first
planetary stage (1) also forming the sun gear of the second stage (2),
the planetary gears (4A-4C, 8A-8C) of both of the first and the second
stages (1, 2) being guided by a common planet carrier (10; 10'), produced
from a casting material, which accommodates the planetary gears (4A-4C)
of the first stage (1) at an axial offset (xS) with respect to the
planetary gears (8A-8C) of the second stage (2), the planet carrier (10;
10') being designed as one-piece such that pockets (11A-11C; 11A'-11D')
are respectively disposed in the planet carrier (10; 10') for receiving
the planetary gears (4A-4C) of the first stage (1) at an offset angle
(αVersatz; αVersatz1,2) in a circumferential
direction to pockets (12A-12C; 12A'-12C') for receiving the planetary
gears (8A-8C) of the second stage (2) so that the pockets being formed
during casting using slides.

9. The planetary gearbox according to claim 8, wherein the offset angle
(α.sub.αversatz; αVersatz1,2) is in a range
of between 20.degree. to 70.degree..

10. The planetary gearbox according to claim 8, wherein each of the
pockets (11A'-11D', 12A'-12C') is formed by an individual slide.

11. The planetary gearbox according to claim 8, wherein webs (15A-15C)
are provided in a circumferential direction between the pockets (12A-12C)
for receiving the planetary gears (8) of the second stage (2), and
openings (14A-14C) for manufacturing the pockets (11A-11C) of the first
stage (1).

12. The planetary gearbox according to claim 8, wherein that the first
stage (1) and the second stage (2) comprise a different numbers of
planetary gears (4A-4C, 8A-8C).

13. The planetary gearbox according to claim 8, wherein the planet
carrier (10; 10') is a high pressure die casting.

14. An automatic transmission of a motor vehicle, the automatic
transmission comprising: at least one planetary gearbox comprising first
and second stages (1, 2), each provided with a sun gear (3), a ring gear
(5, 9) and interposed planetary gears (4A-4C, 8A-8C), the ring gear (5)
of the first planetary stage (1) also forming the sun gear of the second
stage (2), the planetary gears (4A-4C, 8A-8C) of both of the first and
the second stages (1, 2) being guided by a common planet carrier (10;
10'), produced from a casting material, and accommodating the planetary
gears (4A-4C) of the first stage (1) at an axial offset (xS) to the
planetary gears (8A-8C) of the second stage (2), the planet carrier (10;
10') being designed as one-piece, such that pockets (11A-11C; 11A'-11D')
are respectively disposed in the planet carrier (10; 10') for receiving
the planetary gears (4A-4C) of the first stage (1) at an offset angle
(αVersatz; αVersatz1,2) in a circumferential
direction to the pockets (12A-12C; 12A'-12C') for receiving the planetary
gears (8A-8C) of the second stage (2), and the pockets being formed
during casting using slides.

15. A planetary gearbox for an automatic transmission of a motor vehicle,
the planetary gearbox comprises: first and second stages (1, 2) and each
of the first and the second stages (1, 2) comprising a sun gear (3), a
ring gear (5, 9) and interposed planetary gears (4A-4C, 8A-8C), the ring
gear (5) of the first planetary stage (1) forming the sun gear of the
second stage (2), the planetary gears (4A-4C, 8A-8C) of the first and the
second stages (1, 2) being supported by a common planet carrier (10;
10'), which is produced from a casting material as a single piece, the
planetary gears (4A-4C) of the first stage (1) being axially offset with
respect to the planetary gears (8A-8C) of the second stage (2) by an
axial offset (xS), the planet carrier (10; 10') comprising first
pockets (11A-11C; 11A-11D') receiving the planetary gears (4A-4C) of the
first stage (1) and second pockets (12A-12C; 12A'-12C') receiving the
planetary gears (8A-8C) of the second stage (2), the first pockets
(11A-110; 11A'-11D') and the planetary gears (4A-4C) of the first stage
(1) being offset, in a circumferential direction, with respect to the
second pockets (12A-12C; 12A'-12C') and the planetary gears (8A-8C) of
the second stage (2) by a circumferential offset angle
(αVersatz; αVersatz1,2) such that the first and the
second pockets (11A-11C; 11A'-11D', 12A-12C; 12A'-12C') being formed
using slides during casting.

16. The planetary gearbox according to claim 15, wherein the
circumferential offset angle (αVersatz;
αVersatz1,2) is within a range of about 20.degree. to
70.degree..

[0002] The invention relates to a planetary gearbox for an automatic
transmission of a motor vehicle, comprising two stages, each provided
with a sun gear, a ring gear and interposed planetary gears, wherein the
ring gear of the first planetary stage also forms the sun gear of the
second stage, and the planetary gears of both stages are guided by a
common planet carrier made of a cast material, which accommodates the
planetary gears of the first stage at an axial offset to the planetary
gears of the second stage.

BACKGROUND OF THE INVENTION

[0003] Automatic transmissions for motor vehicles having gearboxes
comprising nested planetary gear stages are known, wherein the gearboxes'
power can be transferred between one inner lying sun gear, two planetary
stages and one outer lying ring gear. The planetary stages can be
disposed offset to each other in the axial direction due to the tight
construction space in this automatic transmission.

[0004] The document U.S. Pat. No. 5,503,605 A discloses such a planetary
gearbox for an automatic transmission in which planetary gears of a first
stage are engaged with an inner lying sun gear and with an inner gearing
of a first ring gear. This ring gear of the first planetary gear stage
has a further gearing at its outer circumference by means of which it is
in effective engagement with planetary gears of a second planetary gear
stage, which in turn mesh with an outer lying ring gear. The planetary
gears of both planetary stages are disposed aligned behind one another in
the radial direction guided by a common planet carrier, where the
planetary gears of the first stage are disposed offset in the axial
direction to the planetary gears of the second stage due to the
prevailing conditions of the construction space. In addition, the planet
carrier is composed of two individual pieces, each of which accommodate
the planetary gears of a stage and are joined together in the area of the
first planetary gear stage.

[0005] Furthermore, a planet carrier of a planetary gearbox can be
produced by means of a primary shaping manufacturing process, as is
generally known.

[0006] The two piece design of the planet carrier has the problem that the
planet carrier must be joined together in an additional assembly step,
which increases the expense, and reduces the load capacity of the carrier
in this region. However, manufacturing such a planet carrier as one piece
would make the production process much more difficult because the
arrangement of the planetary gears forms an undercut. Therefore, it is
necessary either to use an expensive casting procedure in which the
undercut pockets of the first stage are formed using a melt-out core, or
to machine cut the pockets after the casting. Both variants significantly
increase the cost of production.

SUMMARY OF THE INVENTION

[0007] Therefore, the problem addressed by the current invention is to
create a planetary gearbox having nested planetary stages for an
automatic transmission, in which a planet carrier guiding the planetary
gears is implemented as one piece, while at the same time reducing the
production costs for producing this planet carrier.

[0008] The invention comprises the technical teaching that the planet
carrier is implemented as one piece so that each of the pockets in the
planet carrier for accommodating the planetary gears of the first stage
are disposed at an angle offset in the circumferential direction to the
pockets for accommodating the planetary gears of the second stage, so
that it is possible to form the pockets during casting using slides. The
pockets of each planetary gear can be demolded using radial slides due to
this design of the relative offset of the planetary gears of the two
stages to each other. Consequently, it is possible to manufacture the
planet carrier of the planetary gearbox according to the invention using
a conventional casting process and at low cost.

[0009] The offset angle is the angle enclosed between lines connecting
adjacent receiving bores for bolts of the planetary gears with a center
point of the planet carrier.

[0010] According to one embodiment of the invention, the offset angle lies
in the range of 20° to 70°. Selecting an offset angle in
this range between the respective pockets of the first and second stage
has the advantage that a pocket of the first stage can be formed together
with a pocket of the second planetary gear stage using a radial slide. As
a result, the number of slides that are required during casting is
reduced.

[0011] In a further development of the invention, every pocket can be
formed by means of an individual slide. This advantageously results in
each pocket being optimally shaped with respect to its contour and
therefore, with respect to strength, and an optimal shape and smooth
running of the planet carrier.

[0012] In one embodiment of the present invention, there are webs in the
circumferential direction, in each case between the pockets for
accommodating the planetary gears of the second stage and the openings
for manufacturing the pockets of the first stage. This has the advantage
that the stiffness of the planet carrier can be significantly increased
by the formed webs in this region.

[0013] Correspondingly, in a further advantageous embodiment of the
invention, the first and second stage comprise different numbers of
planetary gears. As a result, each planetary stage can be individually
adapted to the torques to be transmitted by selecting an appropriate
number of planetary gears, whereby the number of planetary gears can be
reduced, thereby reducing the production costs of the planetary gearbox.

[0014] The planet carrier is expediently designed as a high pressure die
casting. This means that the planet carrier can be produced with greater
precision.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Additional measures improving the invention are represented in the
following in more detail together with the description of preferred
embodiments of the invention based on the figures.

[0016] They show:

[0017] FIG. 1 a sectional representation of a planetary gearbox according
to the invention according to a first embodiment, cut along the line 1-1
in FIG. 2;

[0018] FIG. 2 a cross section of the planetary gearbox, cut along the line
2-2 in FIG. 1; and

[0019] FIG. 3 a cross section of the planet carrier of a planetary gearbox
according to the invention, according to a second embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] FIG. 1 shows a sectional representation of a planetary gearbox
according to the invention according to a first embodiment that is
comprised of two nested stages 1 and 2. The first stage 1 comprises an
inner lying sun gear 3 that is in effective engagement with a ring gear 5
via three planetary gears 4A-4C, of which only the planet gear 4C can be
seen in this view due to the progression of the sectional cut. This ring
gear 5, in addition to an inner gearing 6 for contacting the planetary
gears 4A-4C of the first stage 1, comprises an outer gearing 7 on the
outer circumference by means of which the ring gear 5 engages with three
planetary gears 8A-8C of the second stage 2, and as a result forms the
sun gear for the second stage 2. The planetary gears 8A-8C, in turn, are
in effective engagement with an outer lying second ring gear 9. By using
this nested design of the planetary gearbox in an automatic transmission
of a motor vehicle in a manner known to a person skilled in the art, the
desired rotational speed and torque is transmitted by selective actuation
of clutch elements, not shown.

[0021] The planetary gears 4A-4C of the first stage 1 and the planetary
gears 8A-8C of the second stage 2 are guided by a common planet carrier
10 that accommodates the planetary gears 4A-4C at an axial offset xS
with respect to the planetary gears 8A-8C, in order to maintain a compact
planetary gearbox, and thereby to enable a space saving installation in
the space of an automatic transmission. In the process, the planet
carrier 10 is implemented as a one piece high pressure die cast part,
where the planetary gears 4A-4C and 8A-8C are each disposed offset to
each other in the circumferential direction, in order to make demolding
possible during the casting process using radial slides, despite the
undercut in the area of the planetary gears 4A-4C due to the axial offset
xS.

[0022] FIG. 2 shows a cross section of the planetary gearbox according to
the invention from FIG. 1; here the offset in the circumferential
direction between the planetary gears 4A-4C and 8A-8C is clearly
indicated. As seen in the figure, pockets 11A to 11C, intended for
accommodating the planetary gears 4A-4C of the first stage 1, are located
in the radial inner region of the planet carrier 10, and are each
disposed at an offset angle αVersat to pockets 12A to 12C that
are disposed in the outer radial region of the planet carrier 10, and are
intended for accommodating the planetary gears 8A-8C of the second stage
2. As a result of this offset angle αVersatz, it is possible
to demold the pockets during the casting process using radial slides,
despite the axial offset xS between the planetary gears 4A-4C and
8A-8C of the two stages 1 and 2. In the present case, the offset angle
αVersatz is selected to be small so that pockets 11A to 11C
and the pockets 12A to 12C can each be demolded in pairs using a common
radial slide, as is shown for example by the substitute contour 13 of a
radial slide. In addition, this contour 13 is formed so that webs 15A to
15C are defined in each case between the pockets 12A to 12C for
accommodating the planetary gears 8A-8C, and openings 14A to 14C that are
built into the radial outer region of the planet carrier 10 during
demolding for manufacturing pockets 11A to 11C. The strength of the
planet carrier 10 can be significantly increased in this area by means of
these webs 15A to 15C.

[0023] FIG. 3 shows the cross section of a planet carrier 10' as a single
piece of an alternative embodiment of the planetary gearbox according to
the invention. In contrast to the variant described before, in this case
four pockets 11A' to 11D', at the inner radial region of the planet
carrier 10', are provided for four planetary gears, while in the region
of the outer circumference of the planet carrier 10' as with the prior
variant, there are three chambers 12A' to 12C' for accommodating three
planetary gears. Due to the different numbers of planetary gears to be
guided in the inner radial region and outer radial region of the planet
carrier 10', different offset angles αVersatz1 and
αVersatz2 are formed between each of the pockets 11A' to 11 D'
and 12A' to 12C'. Furthermore, all pockets 11A' to 11D' and 12A' to 12C'
are demolded by means of individual radial slides.

[0024] It is possible to significantly reduce the production costs due to
the shape of the planet carrier 10 or 10' of the planetary gearbox
according to the invention, because the placement of the pockets 11A to
11C and 12A to 12C or 11A' to 11D' and 12A' to 12C' make it possible to
completely demold using radial slides.